5 ms·
Where are the L1 caches?
by SamPutnam 9y ago
Where are the L1 caches?
- saagarjha 9y agoI believe each core had its own L1 cache, hence why it’s not possible to see on the diagram.
- brucedawson 9y agoI think the L1 caches are the per-core blue blobs visible in this die shot: https://randomascii.files.wordpress.com/2018/01/xbox360_processor_die-fixed.jpg https://randomascii.files.wordpress.com/2018/01/xbox360_proc... but I'm not sure.
- saagarjha 9y agoIt could be. In any case that image isn’t labeled, so there’s no way to know for sure without another source.
- readittwice 9y agoIs there a way to "recognize" this? For example why the blue blobs and not the green ones?
- MBCook 9y agoCache/RAM always looks like basically solid colors because it’s so densely packed with a repeating structure. How would you know it’s not the green stuff? I don’t know, perhaps by size. I would imagine the green stuff is some other kind of cache or memory (op cache? TLB buffers? patchy SRAM). This is what I know from seeing these shots online for years. I’m no expert by any means.
- brucedawson 9y agoThe green stuff might have been the VMX register files - those things were pretty huge (128 registers per thread, each register 16 bytes, so 212816=4 KiB per core). While the L1 cache was higher capacity (32 KiB) as a general rule of thumb faster memory uses more die area per bit. But I seem to remember being told that the green areas were the VMX pipelines. I don't remember clearly, and the hardware people I asked at the time were uncertain - they were too far removed from that aspect of the hardware. The other reason to assume that the blue is the caches is because it is closer to the cross-bar and the cross-bar is what connects the cores to the L2. Incoming data from the L2 goes first to the L1 caches so they would logically be on that side.